Compressive wedge cleaving of optical fibers

ABSTRACT

Lengths of an optical fiber may be broken apart from one another while a cross-sectional region of the optical fiber is in a state of multi-axial compressive stress, and the multi-axial compressive stress extends across the optical fiber. The breaking can include propagating a crack across the optical fiber. The crack can be positioned in sufficiently close proximity to the cross-sectional region so that the multi-axial compressive stress restricts the crack from penetrating the cross-sectional region. At least a portion of the optical fiber may be in tension during the breaking.

PRIORITY APPLICATION

This application claims the benefit of priority under 35 U.S.C. §119 ofU.S. Provisional Application Ser. No. 62/084,791, filed on Nov. 26,2014, the content of which is relied upon and incorporated herein byreference in its entirety.

BACKGROUND

This disclosure generally relates to optical fibers and, moreparticularly, to methods and systems for cleaving optical fibers.

Optical fibers are useful in a wide variety of applications, includingthe telecommunications industry for voice, video, and datatransmissions. In a telecommunications system that uses optical fibers,there are typically many locations where fiber optic cables that carrythe optical fibers connect to equipment or other fiber optic cables. Toconveniently provide these connections, fiber optic connectors are oftenprovided on the ends of fiber optic cables. The process of terminatingindividual optical fibers from a fiber optic cable is referred to as“connectorization.” Connectorization can be done in a factory, resultingin a “pre-connectorized” or “pre-terminated” fiber optic cable, or inthe field (e.g., using a “field-installable” fiber optic connector).

Regardless of where installation occurs, a fiber optic connectortypically includes a ferrule with one or more bores that receive one ormore optical fibers. The ferrule supports and positions the opticalfiber(s) with respect to a housing of the fiber optic connector. Thus,when the housing of the fiber optic connector is mated with anotherfiber optic connector or adapter, an optical fiber in the ferrule ispositioned in a known, fixed location relative to the housing. Thisallows an optical communication to be established when the optical fiberis aligned with another optical fiber provided in the mating component(the other fiber optic connector or adapter).

The bores of the ferrule in a fiber optic connector extend to a front ofthe ferrule. With such a design, an optical fiber can be inserted intoand passed through the ferrule. Either before of after securing theoptical fiber relative to the ferrule (e.g., by using a bonding agent inthe bore), an optical surface may be formed on the optical fiber. Oneconventional method of forming an optical surface involves a mechanicalcleaving step followed by several mechanical polishing steps. Suchmethods can be time-consuming and labor-intensive, for example due tothe number of polishing steps that may be required to form an opticalsurface that is both of high quality and in close proximity to the frontof the ferrule. Another conventional method of forming an opticalsurface involves laser cleaving. However, suitable lasers may berelatively expensive, and laser cleaving typically requires polishing.Accordingly, there remains room for improvement.

SUMMARY

One aspect of this disclosure is the provision of a precision processthat is for breaking optical fibers and may be used in place oftraditional cleaving processes, wherein the newly provided process canbe relatively low cost, and may also be readily used in the field.

According to one embodiment of this disclosure, a method for at leastseparating lengths of an optical fiber from one another comprisesbreaking the lengths of the optical fiber apart from one another while across-sectional region of the optical fiber is in a state of multi-axialcompressive stress, and the multi-axial compressive stress extendsacross the optical fiber, wherein the breaking is comprised ofpropagating at least one crack across the optical fiber, and the atleast one crack being positioned in sufficiently close proximity to thecross-sectional region so that the multi-axial compressive stressrestricts the at least one crack from penetrating the cross-sectionalregion. At least a portion of the optical fiber may be in tension duringthe breaking.

The method may further comprise causing the multi-axial compressivestress in the cross-sectional region. For example, the causing of themulti-axial compressive stress may be comprised of applying radialcontact pressure against at least part of the annular portion of theoutermost surface of the optical fiber. As another example, the causingof the multi-axial compressive stress may be comprised of wedging thecross-sectional region at least partially into a bore of a ferrule. Thewedging may be comprised of causing relative movement between the boreand at least one incline defined by the outermost surface of the opticalfiber. The wedging may also be comprised of forming at least one cracknucleation site in the optical fiber, so that the at least one cracknucleation site is proximate both the outer surface of the optical fiberand an opening to the bore. The breaking may be comprised of initiatingthe at least one crack at the at least one crack nucleation site.

In accordance with another embodiment, a method for at least separatinglengths of an optical fiber from one another comprises: causingcompressive radial stress substantially throughout a cross-sectionalregion of the optical fiber, wherein the cross-sectional region extendscrosswise to the lengthwise axis of the optical fiber, and thecross-sectional region includes an annular portion of an outermostsurface of the optical fiber; causing tension in at least a portion ofthe optical fiber; and breaking the lengths of the optical fiber apartfrom one another, wherein the breaking is comprised of propagating atleast one crack across the optical fiber at a position between thelengths, and the at least one crack being positioned in sufficientlyclose proximity to the cross-sectional region so that the compressiveradial stress restricts the at least one crack from penetrating thecross-sectional region, and wherein the breaking occurs while both thecompressive radial stress is present substantially throughout thecross-sectional region, and the tension is present in at least theportion of the optical fiber.

The causing of the compressive radial stress may be comprised ofmounting the optical fiber to a ferrule. The mounting may comprisecausing relative movement between the optical fiber and the ferrule, sothat there is an engaging between the ferrule and the optical fiber, andthe engaging comprises there being opposing face-to-face contact betweenat least a bore of the ferrule and an incline in the annular portion ofthe outermost surface of the optical fiber, wherein the incline isinclined relative to the lengthwise axis of the optical fiber. Themounting may further comprise forming at least one crack nucleation sitein the optical fiber, so that the at least one crack nucleation site isproximate both the outer surface of the optical fiber and an opening toa bore of a ferrule. The breaking may be comprised of initiating the atleast one crack at the at least one crack nucleation site.

According to another embodiment, a method for at least separatinglengths of an optical fiber from one another comprises: inserting anoptical fiber through a bore of a ferrule, wherein the optical fiberincludes a cross-sectional region, and the cross-sectional regionincludes an annular portion of an outermost surface of the opticalfiber; forming at least one incline in the annular portion of theoutermost surface of the optical fiber while the optical fiber extendsthrough the bore, wherein the forming is carried out so that the atleast one incline is inclined relative to the lengthwise axis of theoptical fiber; causing relative movement between the optical fiber andthe ferrule so that the cross-sectional region is wedged at leastpartially into the bore and the cross-sectional region is placed in astate of compressive stress, and at least a portion of the optical fiberis in tension; and breaking the lengths of the optical fiber apart fromone another while the cross-sectional region is wedged at leastpartially into the bore and in the state of compressive stress, andwhile the at least the portion of the optical fiber is in tension, sothat a terminal end of the optical fiber is formed at a predeterminedposition, and the predetermined position is both positioned proximatethe opening of the bore, and positioned outside of the bore.

The causing of the relative movement may be comprised of pulling. Themethod may further comprise adhesively mounting the optical fiber in thebore while at least the portion of the optical fiber is in tension. Thebreaking may be carried out so that the terminal end as a whole iswithin about 10 um from the opening of the bore.

In some embodiments, the multi-axial compressive stress may consistsessentially of biaxial compressive stress extending substantiallythroughout the cross-sectional region.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the technical field of optical communications. It is to beunderstood that the foregoing general description, the followingdetailed description, and the accompanying drawings are merely exemplaryand intended to provide an overview or framework to understand thenature and character of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding, and are incorporated in and constitute a part of thisspecification. The drawings illustrate one or more embodiments, andtogether with the description serve to explain principles and operationof the various embodiments. Features and attributes associated with anyof the embodiments shown or described may be applied to otherembodiments shown, described, or appreciated based on this disclosure.

FIG. 1 is a perspective view of an example of a fiber optic cableassembly that includes a fiber optic connector;

FIG. 2 is an exploded perspective view of the connector of FIG. 1;

FIG. 3 is an enlarged, schematic, partially cross-sectional side view ofa representative portion of a ferrule of the connector of FIG. 1 havinga representative optical fiber of the cable of FIG. 1 extendingtherethrough, in accordance with an exemplary embodiment of thisdisclosure;

FIG. 4 is enlarged, schematic side view of a bulge formed in a portionof the optical fiber of FIG. 3, and associated electrodes and arcs forforming the bulge are also schematically shown, in accordance with theexemplary embodiment;

FIG. 5 is an enlarged, schematic, partially cross-sectional side viewsimilar to FIG. 3, except for showing the bulge wedged into a bore ofthe ferrule, in accordance with the exemplary embodiment;

FIG. 6 is a schematic, isolated, end elevation view of a cross-sectionalregion of a wedged zone of the bulge of FIG. 5 being exposed toinwardly-directed radial force components, in accordance with theexemplary embodiment; and

FIG. 7 is an enlarged, schematic side view of the representativeportions of the ferrule and optical fiber after breaking, and apolishing pad is also schematically shown, in accordance with theexemplary embodiment.

DETAILED DESCRIPTION

Various embodiments will be further clarified by examples in thedescription below. In general, the description relates to methods ofbreaking optical fibers that may be used in place of at least some priorcleaving processes. The methods may be part of a cable assembly processfor a fiber optic cable. That is, the methods may be part of terminatingoptical fibers from a fiber optic cable with a fiber optic connector toform a cable assembly.

One example of a fiber optic connector (“connector”) 10 for such a cableassembly is shown in FIGS. 1 and 2, and this type of connector may bereferred to as a multi-fiber push on (MPO) connector, which includes apush-pull latch, and incorporates a mechanical transfer (MT) ferrule.These connectors can achieve a very high density of optical fibers,which reduces the amount of hardware, space, and effort to establish alarge number of interconnects. A general discussion of the connector 10will be provided, followed by a discussion of an example of a method forprecisely breaking optical fibers. Although the connector 10 is shown inthe form of a MPO-type connector, the methods described below may beapplicable to processes involving different fiber optic connectordesigns, such as SC, ST, LC, and other single fiber or multifiberconnector designs, and different types of fiber optic cable assemblies.

As shown in FIG. 1, the connector 10 may be installed on a fiber opticcable (“cable”) 12 to form a fiber optic cable assembly 14. Theconnector 10 includes a ferrule 16, a housing 18 received over theferrule, a slider 20 received over the housing, and a boot 22 receivedover the cable 12. The ferrule 16 is spring-biased within the housing 18so that a front portion 24 of the ferrule extends beyond a front end 26of the housing. Optical fibers (“fibers”) carried by the cable 12 extendthrough respective bores 28 in the ferrule 16 before terminating at ornear a front end face 30 of the ferrule. There may be a single row oftwelve bores 28, although it is within the scope of this disclosure forthere to be a greater or lesser number of each of the rows and bores.The fibers are secured within the ferrule 16 using an adhesive material(e.g., epoxy) and can be presented for optical coupling with fibers of amating component (e.g., another fiber optic connector, not shown) whenthe housing 20 is inserted into an adapter, receptacle, or the like.

As shown in FIG. 2, the connector 10 further includes a ferrule boot 32,guide pin assembly 34, spring 36, retention body (“crimp body”) 38, andcrimp ring 40. The ferrule boot 32 is received in a rear portion 42 ofthe ferrule 16 to help support the fibers extending to the bores 28. Theguide pin assembly 34 includes a pair of guide pins 44 extending from apin keeper 46. Features on the pin keeper 46 cooperate with features onthe guide pins 44 to retain portions of the guide pins 44 within the pinkeeper 46. When the connector 10 is assembled, the pin keeper 46 ispositioned against a back surface of the ferrule 16, and the guide pins44 extend through pin holes 48 (FIG. 1) provided in the ferrule 16 so asto project beyond the front end face 30. The presence of the guide pins44 means that the connector 10 is in a male configuration. In a femaleconfiguration the guide pins 44 are not present. As another example, theguide pin assembly 34 may be omitted, such as when other provisions maybe made for alignment, as may be the case when the ferrule 16 includesmolded-in post and hole alignment features.

Both the ferrule 16 and guide pin assembly 34 (if present) are biased toa forward position relative to the housing 18 by the spring 36. Morespecifically, the spring 36 is positioned between the pin keeper 46 anda portion of the crimp body 38. The crimp body 38 is inserted into thehousing 18 when the connector 10 is assembled. The crimp body 38includes latching arms 50 that engage recesses 52 in the housing 18. Thespring 36 is compressed by this point and exerts a biasing force on theferrule 16, such as via the pin keeper 46. The rear portion 42 of theferrule 16 defines a flange that interacts with a shoulder or stopformed within the housing 18 to retain the rear portion 42 within thehousing 18.

In a manner not shown in the figures, aramid yarn or other strengthmembers from the cable 12 are positioned over a rear end portion 54 ofthe crimp body 38 that projects rearwardly from the housing 18. Thearamid yarn is secured to the end portion 54 by the crimp ring 40, whichis slid over the end portion 54 and deformed after positioning thearamid yarn. The boot 22 covers this region, as shown in FIG. 1, andprovides strain relief for the fibers by limiting the extent to whichthe connector 10 can bend relative to the cable 12.

Variations of these aspects will be appreciated by persons skilled inthe design of fiber optic cable assemblies. Again, the embodiment shownin FIGS. 1 and 2 is merely an example of a fiber optic connector thatmay be used in the methods described below. The general overview hasbeen provided simply to facilitate discussion.

With this in mind, the one or more fibers of the cable 12 may be mountedto the ferrule 16 prior to the connector 10 being completely assembled,and a method of mounting and breaking the fibers is described in thefollowing, in accordance with an embodiment of this disclosure. Asschematically shown in FIG. 3, a bare (e.g., “stripped”) portion of arepresentative fiber 27 extends through a representative bore 28 of theferrule 16, and an adhesive material, such as epoxy 59, may be withinthe bore 28 for use in fixedly connecting the fiber in the bore, as willbe discussed in greater detail below. The fiber 27 may be insertedthrough the bore 28 so that the ferule 16 is positioned between thecable 12 (FIG. 1) and a terminal end 58 of the fiber. More specifically,the terminal end 58 of the fiber 27 may be inserted through the bore 28so that a first length 60 of the fiber is passed through the bore and asecond length 62 of the fiber extends outwardly from an opening 64 ofthe bore. At this stage in the process, any boundaries between the firstand second lengths 60, 62 of the fiber 27 can be indiscernible.Nonetheless, the first and second lengths 60, 62 are introduced at thistime as a prelude to the more detailed discussions about them in thefollowing.

While the second length 62 of the fiber 27 extends outwardly from theopening 64 of the bore 28 as shown in FIG. 3, a bulge 66 (FIG. 4) may beformed in the fiber at the transition between the first and secondlengths 60, 62 of the fiber. The bulge 66 is formed at a distance fromthe ferrule 16, so that the bulge is spaced apart from the ferrule. Thebulge 66 may be formed by localized heating of the fiber 27. Thelocalized heating for forming the bulge 66 may be carried out throughthe use of any suitable heat source such as, for example, a flame, laserbeam or electrical arcs.

In the example schematically shown in FIG. 4, the localized heating forforming the bulge 66 may be provided by one or more high-temperaturefusion arc(s) 68 provided between opposing electrodes 70. The energyfrom the heat source, such as the arc(s) 68, acts to locally soften thefiber 27 to form a locally deformed region that may be referred to asthe bulge 66. It is believed that surface tension effects caused by thelocalized heating cause an increase in the fiber diameter, therebycreating the bulge 66. The bulge 66 has a diameter that is larger thanthe normal diameter of the fiber 27.

As schematically shown in FIG. 4, the bulge 66 may have a substantiallycylindrical portion 71 positioned between and contiguous with a pair ofsubstantially frusto-conical portions 72, 74, or the like. Thefrusto-conical portion 72 may be referred to as, for example, a wedge orwedged zone, or the like, for reasons that will become further apparentin the following. As schematically illustrated by a pair of paralleldashed lines in FIG. 4, the second length 62, or more specifically theinner frusto-conical portion 72, may be characterized as including athree-dimensional (e.g., thick) cross-sectional region 76 that extendsboth along and crosswise to a lengthwise axis 78 of the fiber 27. InFIG. 4, the pair of parallel dashed lines illustrate the opposite endsof the cross-sectional region 76. The cross-sectional region 76 may beconfigured so that it extends substantially perpendicularly to thelengthwise axis 78. The bulge 66 may be formed in a manner so as not tosubstantially affect the wave-guiding properties of the second length 62of the fiber 27, wherein the second length of the fiber includes thecross-sectional region 76.

The cross-sectional region 76 of the embodiment shown includes aninclined, substantially frusto-conical, outermost engagement surface 80that extends around and along the lengthwise axis 78 of the fiber 27.The engagement surface 80 is inclined relative to the lengthwise axis78. Accordingly and as best understood with reference to FIG. 4, theengagement surface 80 may be characterized as including oppositeinclines 82 in a side elevation view. The inclines 82, which are partsof the substantially frusto-conical engagement surface 80, extend alongand are inclined relative to the lengthwise axis 78. In accordance withan embodiment, FIG. 4 can be schematically illustrative of each of rightand left side elevation views, and top and bottom plan views of thebulge 66. FIG. 4 is schematic because, for example, at least some of thesurfaces of the bulge 66 are typically not perfectly cylindrical orperfectly frusto-conical, as discussed in greater detail below. Indeed,the surfaces of the bulge 66 may be somewhat rounded in the directionalong the lengthwise axis 78.

In the embodiment illustrated in the drawings, the bulge 66 is formed ina manner so that the cross-sectional region 76 has a maximum outerdiameter that is only slightly larger than the diameter of the bore 28(FIG. 3). Referring to FIG. 5, the cross-sectional region 76 with itsengagement surface 80 may be characterized as being a fiber-to-ferruleinterface region that is for being in opposing face-to-face contact orengagement with the ferrule 16. More specifically, after the bulge 66 isformed at a distance from the ferrule 16, a method of this disclosureincludes causing relative movement between the fiber 27 and the ferrule,so that the cross-sectional region 76 of the second length 62 is wedgedat least partially into the bore 28 of the ferrule. This relativemovement between the fiber 27 and the ferrule 16 may be provided, forexample, through manual action or any other suitable action. The manualor other suitable action may include pulling the cable 12 (FIG. 1) orfiber 27 so that the cross-sectional region 76 moves toward the opening64 (FIG. 3) of the bore 28, and the engagement surface 80, including theinclines 82, engages into opposing face-to-face contact with the ferrule16. The pulling of the cable 12 or fiber 27, and the associated tensionin the second length 62 of the fiber, is schematically illustrated by anarrow 84 in FIG. 5.

Partially reiterating from above, the maximum outer diameter of thecross-sectional region 76 may initially be only slightly larger than thediameter of the bore 28. At the point of engagement between the wedgedcross-sectional region 76 and the surface of the bore 28, the amount ofdiameter increase for the bore may be about 0.5% for single modeferrules, and about 2% to about 4% for multimode ferrules.

The engagement surface 80 of the cross-sectional region 76 engaging intoopposing face-to-face contact with the ferrule 16 may comprise, consistessentially of, or consist of the engagement surface of thecross-sectional region engaging into opposing face-to-face contact withthe surface of the bore 28 proximate the opening 64 (FIG. 3) of thebore. The surface of the bore 28 can be the cylindrical surface of theferrule 16 that defines the bore. More specifically, the opposingface-to-face contact may be defined at least between a substantiallycircular portion of the engagement surface 80 and a substantiallycircular portion of the surface of the bore 28. Even though a largeportion of the central region of the bulge 66 may be distorted ratherthan being perfectly cylindrical or perfectly frusto-conical, there is atransition length between the central region of the bulge 66 and thenon-bulged portion of the fiber 27, and the cross-sectional region 76,including the substantially circular portion of the engagement surface80, is typically located in this transition length. Since the diameterof the non-bulged portion of the fiber 27 is typically only slightlysmaller than the diameter of the bore 28 (typically less than 0.5 umclearance on the radius), when the inner frusto-conical portion 72 ispulled back into the bore, only a small part of the inner frusto-conicalportion extends into the bore before the contact between the engagementsurface 80 and the surface of the bore arrests the relative movementbetween the fiber 27 and the ferrule 16.

As additional examples, the relative movement between the fiber 27 andferrule 16 may cause and/or include, for example, the innerfrusto-conical portion 72 at least partially entering the bore 28, atleast one of the inclines 82 engaging the bore, relative sliding betweenthe incline and the bore, forming an interference fit between thecross-sectional region and the surface of bore, and placing at least aportion of the cross-sectional region 76 in a state of multi-axialcompressive stress. The multi-axial compressive stress in the wedgedcross-sectional region 76 may be more specifically in the form ofbiaxial compressive stress, as will be discussed in greater detailbelow.

The ferrule 16 and, thus, the surface of the bore 28, may be made of arelatively rigid and hard ceramic material, or any other suitablematerial. In this regard and further regarding the illustratedembodiment's wedged engagement between the engagement surface 80 of thecross-sectional region 76 and the bore 28, the multi-axial compressivestress in the wedged cross-sectional region is caused by the surface ofthe bore applying contact pressure against the engagement surface of thewedged cross-sectional region. The surface of the bore 28 applying theradial contact pressure against the engagement surface 80 of the wedgedcross-sectional region 76 may include: applying radial contact pressureagainst at least part of the engagement surface 80; and/or applyingradial contact pressure against substantially all of a substantiallycircular portion of the engagement surface 80.

For the embodiment illustrated in the drawings, due to the substantiallyfrusto-conical, outermost engagement surface 80 being inclined relativeto the lengthwise axis 78 of the fiber 27, each contact force applied bythe surface of the bore 28 against the engagement surface 80 can beresolved or otherwise be theoretically divided into a pair ofindependent vectors or force components that extend at right angles toeach other. One of the components of the pair of force components is anaxial force component that extends substantially parallel to thelengthwise axis 78. In contrast, the other force component of the pairof force components is a radial force component that extends toward andsubstantially perpendicular to the lengthwise axis 78. For example, FIG.6 schematically illustrates, with radially inwardly pointing arrows 86,a representative series or sampling of the inwardly-directed radialforce components that are applied against the engagement surface 80 ofthe wedged cross-sectional region 76 by the surface of the bore 28. Inthe embodiment illustrated in the drawings, it is the radial forcecomponents 86 of the contact force applied by the surface of the bore 28against the engagement surface 80 that cause the compressive stress inthe wedged cross-sectional region 76 to be biaxial compressive stress.

In the embodiment with the biaxial compressive stress, for the directionof (i.e., along) the lengthwise axis 78, there is substantially zerocompressive stress in the wedged cross-sectional region 76. Therefore,the biaxial compressive stress can be quantified through the use of atwo-dimensional domain having two coordinate axes, wherein the twocoordinate axes are both perpendicular to the lengthwise axis 78, andthe two coordinate axes are perpendicular to one another. In thisexample, since the compressive stress in the wedged cross-sectionalregion 76 can be quantified solely through the use of a two-dimensionaldomain having two coordinate axes, the compressive stress in the wedgedcross-sectional area is biaxial compressive stress.

Further regarding the cross-sectional 76 area being in a state ofmulti-axial compressive stress, the multi-axial compressive stress mayextend substantially throughout the wedged cross-sectional region. Inaddition, the multi-axial compressive stress may comprise, consistessentially of, or consist of compressive radial stress, wherein thecompressive radial stress may extend substantially throughout the wedgedcross-sectional region 76. As another example, multi-axial compressivestress may comprise, consist essentially of, or consist of biaxialcompressive stress, wherein the biaxial compressive stress may extendsubstantially throughout the wedged cross-sectional region 76.

For the wedged cross-sectional region 76, it is believed that there maytypically be some compressive stress in the direction of (i.e., along)the lengthwise axis 78. Therefore, the multi-axial compressive stress inthe wedged cross-sectional region 76 can include compressive stress inthe direction of the lengthwise axis 78. Nonetheless, for the embodimentshown in the drawings, it is believed that the magnitude of any suchcompressive stress in the direction of the lengthwise axis 78 would beinsignificant as compared to the radial compressive stress, such thatthe multi-axial compressive stress in the wedged cross-sectional region76 may consist essentially of biaxial compressive stress.

As will be discussed in greater detail below, one aspect of thisdisclosure is the provision of a method of forming a break between thefirst and second lengths 60, 62 of the fiber 27, wherein the method mayinclude breaking the first and second lengths apart from one anotherwhile the wedged cross-sectional region 76 is in a state of sufficientmulti-axial compressive stress. In the embodiment illustrated in thedrawings, the magnitude of the multi-axial compressive stress in thewedged cross-sectional region 76 is a function of, for example, both theinclination of the engagement surface 80 and the tension in the secondlength 62 of the fiber 27, wherein this tension is schematicallyillustrated by the arrow 84 in FIG. 5. In one embodiment, the fiber 27is pulled back into the bore 28 under a predetermined amount of tension.For example, the amount of tension 84 in the second length 62 of thefiber 27, while the engagement surface 80 is engaged against the surfaceof the bore 28, may be in a range of from about 50 grams to about 500grams, or in a range of from about 10 grams to about 100 grams.

After the cross-sectional region 76 is wedge into the bore 28, thetension 84 may be maintained while the second length 62 of the fiber 27is bonded to the surface of the bore 28. This bonding may be carriedout, for example, by applying heat to the ferrule 16, so that the heatactivates the heat-activated epoxy 59, or the like. The tension 84 maybe maintained until the epoxy 59 cools. Thereafter, the cooled and rigidepoxy 59 may fixedly secure at least a portion of the second length 62of the fiber 27 in the bore 28 so that the epoxy functions to at leasttemporarily maintain the tension 84.

It is believed that the above-discussed engagement between theengagement surface 80 of the wedged cross-sectional region 76 and theferrule 16, or more specifically the surface or edge of bore 28, maycause the formation of at least one crack nucleation site in the fiber27, so that the at least one crack nucleation site is proximate theopening 28 (FIG. 3) to the bore. The crack nucleation site may be in theform of an imperfection defined at least in the outer surface of thefiber 27. The crack nucleation site may include a nick, scrape, scratch,scuff, score, or the like, or any suitable combinations thereof. Forexample, the one or more crack nucleation sites may extend at leastpartially around, or completely around, the inner frusto-conical portion72. In this regard, a crack nucleation site is schematically illustratedas a score line 88 in FIG. 5. In accordance with an embodiment, FIG. 5is schematically illustrative of each of right and left side views, andtop and bottom plan views; therefore, FIG. 5 may be characterized asbeing schematically illustrative of the score line 88 extendingcompletely around the inner frusto-conical portion 72. Alternatively,the crack nucleation site may be less extensive, such by the score line88, or the like, extending only partially around the innerfrusto-conical portion 72. FIG. 5 is schematic because, for example, anyfeature (e.g., score line 88) that functions as a crack nucleation sitemay not be readily visible to the naked eye, or the like.

As schematically shown in FIG. 5, the score line 88 is positionedbetween a pair of vertical dashed lines. The pair of vertical dashedlines schematically shown in FIG. 5 are for partially demarkingboundaries of the wedged cross-sectional region 76 and a breaking zone90. In the embodiment illustrated in the drawings, the breaking zone 90is where a break occurs in response to a force, such as a breaking forceschematically represented by arrow 92 in FIG. 5, being applied to thefirst length 60 of the fiber 27 while the multi-axial compressive stressin the wedged cross-sectional region 76 is of sufficient magnitude, aswill be discussed in greater detail below.

The left-most vertical dashed line of FIG. 5 may be referred to as aninner dashed line, and the right-most dashed line of FIG. 5 may bereferred to as an outer dashed line. As shown in FIG. 5, the wedgedcross-sectional region 76 is positioned to the left of the score line88, so that the wedged cross-sectional region is positioned between thescore line 88 and the inner dashed line. In contrast, the breaking zone90 includes the score line 88. The breaking zone 90 extends from thescore line 88 to the right, so that the breaking zone extends from thescore line 88 to the outer dashed line of FIG. 5.

The maximum diameter of the bulge 66 may be in a range of from about125% to about 500% of the nominal diameter of the non-bulged portions ofthe fiber 27. As best understood with reference to FIG. 5, the length L1of the cross-sectional region 76 may be in a range of from about 50% toabout 500% of the nominal diameter of the non-bulged portions of thefiber 27. The length L2 of the breaking zone 90 may be in a range offrom about 10% to about 50% of the nominal diameter of the non-bulgedportions of the fiber 27.

The tension 84 may be important for causing the multi-axial compressivestress in the wedged cross-sectional region 76 to be of sufficientmagnitude for causing the break to be positioned in the breaking zone90. The tension 84 may be at least partially maintained by the epoxy 59as discussed above, or the breaking force 92 may be applied prior to theepoxy 59 being solidified and while the tension 84 is maintained in anyother suitable manner. The breaking force 92 may be provided by touchingthe fiber 27 with a finger, a blunt edge of a tool, or with any othersuitable device. For example, a break may be formed as described hereinwithout requiring a laser or a traditional scribe-based cleaving system.

In accordance with an embodiment of this disclosure, a break between thefirst and second lengths 60, 62 of the fiber 27 may be formed in thebreaking zone 90 (while there is sufficient multi-axial compressivestress in the wedged cross-sectional region 76) without requiring anytraditional cleaving or scoring tools. More specifically regarding thisbreaking, the score line 88 in FIG. 5 may also be schematicallyillustrative of one or more cracks 88 that propagate across the fiber 27in response to the breaking force 92 being applied as described above.It is believed that the above-discussed crack nucleation cite(s) (e.g.score line 88) cause one or more cracks 88 to initiate within thebreaking zone 90 in close proximity to the wedged cross-sectional region76, and that the multi-axial compressive stress in the wedgedcross-sectional region 76 at least partially controls the propagation ofeach crack 88 across the fiber 27 by restricting the crack(s) frompenetrating significantly into the wedged cross-sectional region 76, ifat all.

In accordance with the embodiment shown in FIGS. 5 and 7, the crack 88defines the boundary between the first and second lengths 60, 62. Thatis, the crack 88 separates the first and second lengths 60, 62 so that anewly formed fracture surface defines the resulting terminal end 94(FIG. 7) of the second length. As shown in FIG. 7, the terminal end 94may be positioned outside the opening 64 (FIG. 3) of the bore 28, sothat a distance D is defined between the terminal end 94 and both thefront end face 30 of the ferrule 16 and the opening 64 (FIG. 3) of thebore. The distance D may be about 20 um or less, or about 10 um or less,so as to be substantially proximate the opening 64 of the bore 28.

In the wedged configuration shown in FIG. 5, the inner end of thebreaking zone 90 is coplanar with the front end face 30 of the ferrule16, so that breaking zone extends outwardly from the front end face ofthe ferrule. The outer end of the breaking zone 90 may be described asbeing at the same location as the outermost portion of the terminal end94 (FIG. 7) after breaking the lengths 60, 62 apart from one another.FIG. 7 is schematic because, for example, the terminal end 94 typicallyis not in the form of a flat-tipped cylindrical stub. Rather, theterminal end 94 may be in the form of a spike, with one or more tips.Therefore, the outer end of the breaking zone 90 may be described asbeing at the same location as the outermost tip(s) of the spike thatdefines the terminal end 94.

As schematically illustrated in FIG. 7, the terminal end 94 may bepolished by a polishing pad 96, such as through a single-step polishingprocess, to reduce the distance D to about zero, to effectively causethe terminal end 94 to be substantially flush with the front end face 30of the ferrule 16 (e.g., within about +/−200 nm, within about +/−100 nm,within a range of from about +50 nm to about −75 nm, or even within arange of about +/−30 nm in some embodiments). In FIG. 7, arrows 98represent the polishing pad 96 being moved for facilitating thepolishing.

In addition to facilitating breaking as discussed above, thecross-sectional region 76 being wedged into the bore 28 may also causethe wedged cross-sectional region to be centered in the bore 28, whichmay provide additional advantages.

In the above-described embodiment, the multi-axial compressive stress inthe wedged cross-sectional region 76 is provided in association withinclines 82 and a ferrule 16. However, the multi-axial compressivestress in the wedged cross-sectional region 76 may be provided in anyother suitable manner, such as, for example, with a precision clampingtool.

Persons skilled in optical connectivity will appreciate additionalvariations and modifications of the devices and methods alreadydescribed. Additionally, where a method claim below does not explicitlyrecite a step mentioned in the description above, it should not beassumed that the step is required by the claim. Furthermore, where amethod claim below does not actually recite an order to be followed byits steps or an order is otherwise not required based on the claimlanguage, it is not intended that any particular order be inferred.

The above examples are in no way intended to limit the scope of thepresent invention. It will be understood by those skilled in the artthat while the present disclosure has been discussed above withreference to examples of embodiments, various additions, modificationsand changes can be made thereto without departing from the spirit andscope of the invention as set forth in the claims.

What is claimed is:
 1. A method for at least separating lengths of anoptical fiber from one another, comprising: breaking the lengths of theoptical fiber apart from one another while a cross-sectional region ofthe optical fiber is in a state of multi-axial compressive stress, andthe multi-axial compressive stress of the cross-sectional region extendsacross the optical fiber; wherein the breaking is comprised ofpropagating at least one crack across the optical fiber while thecross-sectional region is in the state of multi-axial compressivestress, and the at least one crack being positioned in sufficientlyclose proximity to the cross-sectional region while the cross-sectionalregion is in the state of multi-axial compressive stress so that themulti-axial compressive stress in the cross-sectional region restrictsthe at least one crack from penetrating the cross-sectional region. 2.The method of claim 1, wherein the multi-axial compressive stressconsists essentially of biaxial compressive stress extendingsubstantially throughout the cross-sectional region.
 3. The method ofclaim 1, wherein: the breaking is comprised of forming a terminal end ofthe optical fiber; and the method further comprises polishing theterminal end.
 4. The method of claim 1, further comprising causing themulti-axial compressive stress in the cross-sectional region, whereinthe causing of the multi-axial compressive stress is comprised ofwedging the cross-sectional region at least partially into a bore of aferrule.
 5. The method of claim 4, wherein: the cross-sectional regionincludes an annular portion of an outermost surface of the opticalfiber; the method further comprises forming at least one incline in theannular portion of the outermost surface, so that the at least oneincline is inclined relative to a lengthwise axis of the optical fiber;and the wedging is comprised of causing relative movement between thebore and the at least one incline so that there is relative slidingbetween the bore and the at least one incline.
 6. The method of claim 4,wherein: the wedging is comprised of forming at least one cracknucleation site in the optical fiber, so that the at least one cracknucleation site is proximate both the outer surface of the optical fiberand an opening to the bore; and the breaking is comprised of initiatingthe at least one crack at the at least one crack nucleation site.
 7. Themethod of claim 1, wherein: the multi-axial compressive stress extendssubstantially throughout the cross-sectional region; the cross-sectionalregion extends crosswise to a lengthwise axis of the optical fiber; thecross-sectional region includes an annular portion of an outermostsurface of the optical fiber; the method further comprises causing themulti-axial compressive stress in the cross-sectional region; and thecausing of the multi-axial compressive stress is comprised of applyingradial contact pressure against at least part of the annular portion ofthe outermost surface of the optical fiber.
 8. The method of claim 1,further comprising causing the multi-axial compressive stress in thecross-sectional region, wherein: the cross-sectional region includes anannular portion of an outermost surface of the optical fiber; and thecausing of the multi-axial compressive stress is comprised of applyingradial contact pressure against at least part of the annular portion ofthe outermost surface of the optical fiber.
 9. The method of claim 8,wherein the applying of the radial contact pressure is comprised ofcausing relative movement between the optical fiber and a ferrule, sothat there is an engaging between the ferrule and the optical fiber, andthe engaging comprises there being opposing face-to-face contact betweenat least: a bore of the ferrule, and an incline in the annular portionof the outermost surface of the optical fiber, wherein the incline isinclined relative to a lengthwise axis of the optical fiber.
 10. Themethod of claim 9, wherein: the method further comprises inserting theoptical fiber through the bore, and forming the incline after theinserting of the optical fiber through the bore; and the causing of therelative movement comprises causing the incline to enter the bore afterthe forming of the incline.
 11. The method of claim 9, wherein: theengaging comprises forming at least one crack nucleation site in theoptical fiber, so that the at least one crack nucleation site isproximate both the outer surface of the optical fiber and an opening tothe bore; and the breaking is comprised of the at least one crack beinginitiated at the at least one crack nucleation site.
 12. The method ofclaim 9, wherein at least a portion of the optical fiber is in tensionduring the breaking.
 13. The method of claim 1, wherein: the lengths ofthe optical fiber comprise a first length of the optical fiber and asecond length of the optical fiber; the cross-sectional region, which isin the state of multi-axial compressive stress, is positioned in thesecond length of the optical fiber; and the breaking is furthercomprised of: applying a breaking force to the first length of theoptical fiber at a position spaced from both the at least one crack andthe second length of the optical fiber, and the braking force extendingcrosswise to the first length of the optical fiber.
 14. A method for atleast separating lengths of an optical fiber from one another,comprising: causing compressive radial stress substantially throughout across-sectional region of the optical fiber, wherein the cross-sectionalregion extends crosswise to a lengthwise axis of the optical fiber, andthe cross-sectional region includes an annular portion of an outermostsurface of the optical fiber; causing tension in at least a portion ofthe optical fiber; and breaking the lengths of the optical fiber apart,from one another, wherein: the breaking is comprised of propagating atleast one crack across the optical fiber at a position between thelengths, and the at least one crack being positioned in sufficientlyclose proximity to the cross-sectional region, so that the compressiveradial stress that is present substantially throughout thecross-sectional region restricts the at least one crack from penetratingthe cross-sectional region, and the breaking occurs while both: thecompressive radial stress is present substantially throughout thecross-sectional region, and the tension is present in the at least theportion of the optical fiber.
 15. The method of claim 14, wherein thecausing of the compressive radial stress is comprised of mounting theoptical fiber to a ferrule.
 16. The method of claim 15, wherein themounting comprises forming an interference fit between the optical fiberand the ferrule.
 17. The method of claim 15, wherein the mountingcomprises causing relative movement between the optical fiber and theferrule, so that there is an engaging between the ferrule and theoptical fiber, and the engaging comprises there being opposingface-to-face contact between at least: a bore of the ferrule, and anincline in the annular portion of the outermost surface of the opticalfiber, wherein the incline is inclined relative to a lengthwise axis ofthe optical fiber.
 18. The method of claim 15, wherein: the mountingcomprises forming at least one crack nucleation site in the opticalfiber, so that the at least one crack nucleation site is proximate boththe outer surface of the optical fiber and an opening to a bore of aferrule; and the breaking is comprised of initiating the at least onecrack at the at least one crack nucleation site.
 19. The method of claim14, wherein: the causing of the tension is comprised of causinglengthwise tension in the at least the portion of the optical fiber; andthe breaking occurs while the lengthwise tension is present in the atleast the portion of the optical fiber.
 20. The method of claim 14,wherein: the lengths of the optical fiber comprise a first length of theoptical fiber and a second length of the optical fiber; thecross-sectional region is positioned in the second length of the opticalfiber; and the breaking is further comprised of: applying a breakingforce to the first length of the optical fiber at a position spaced fromboth the at least one crack and the second length of the optical fiber,and the braking force extending crosswise to the first length of theoptical fiber.
 21. A method for at least separating lengths of anoptical fiber from one another, comprising: inserting an optical fiberthrough a bore of a ferrule, wherein the optical fiber includes across-sectional region, and the cross-sectional region includes anannular portion of an outermost surface of the optical fiber; forming atleast one incline in the annular portion of the outermost surface of theoptical fiber while the optical fiber extends through the bore, whereinthe forming is carried out so that the at least one incline is inclinedrelative to a lengthwise axis of the optical fiber; causing relativemovement between the optical fiber and the ferrule so that both: thecross-sectional region is wedged at least partially into the bore andthe cross-sectional region is placed in a state of compressive stress,and at least a portion of the optical fiber is in tension; and breakingthe lengths of the optical fiber apart from one another while thecross-sectional region is wedged at least partially into the bore and inthe state of compressive stress and while the at least the portion ofthe optical fiber is in tension, so that a terminal end of the opticalfiber is formed at a predetermined position, and the predeterminedposition is both: positioned proximate the opening of the bore, andpositioned outside of the bore.
 22. The method of claim 21, wherein thebreaking is carried out so that the terminal end as a whole is withinabout 10 um from the opening of the bore.
 23. The method of claim 21,wherein: the lengths of the optical fiber comprise a first length of theoptical fiber and a second length of the optical fiber; thecross-sectional region, which is in the state of compressive stress, ispositioned in the second length of the optical fiber; and the breakingis further comprised of: applying a breaking force to the first lengthof the optical fiber at a position spaced from both the at least onecrack and the second length of the optical fiber, and the braking forceextending crosswise to the first length of the optical fiber.
 24. Themethod of claim 21, wherein: the at least the portion of the opticalfiber is in lengthwise tension in response to at least thecross-sectional region being wedged at least partially into the bore andthe relative movement between the optical fiber and the ferrule; and thebreaking occurs while the lengthwise tension is present in the at leastthe portion of the optical fiber.
 25. The method of claim 24, wherein:the causing of the relative movement is comprised of pulling; the methodfurther comprises adhesively mounting the optical fiber in the borewhile the at least the portion of the optical fiber is in the lengthwisetension; and the at least the portion of the optical fiber being in thelengthwise tension is further responsive to the optical fiber beingadhesively mounting the in line bore.